Mercury boiler



A. J, NERAD MERCURY BOILER oct. 29, 1940.

Filed June 2l, 1938.

Fig.

Inventor Anthony Nefad Patented Oct. 29, 1940 :UNITED STATES 2,219,935 MERCURY BolLE'a Anthony J. Nerad, Schenectady, N. Y., assigner to General Electric Company,

New York n a corporation of Application June 21, 1938, Serial No. 214,987

28 Claims. The present invention is a continuation in part of my application Serial No. 48,859,"led No- .'vember 8, 1935, and relates to mercury boilers,

generally to vessels made from ferrous metal for heating mercury in which the mercury comes into contact with thevferrous metal at Vhigh temperatures, for example, temperatures of theorder of 1000" F. It has been found that'mercury at high 'Y temperatures, especiallyat the operating temrangements and methods of operating'lmercury boilers of 'this type arejmore fully disclosed inVV my Patent 1,964'3593, filed YJuly 1, 1933, and asv signed to the same assigneeV as the present appli:U

cation.

Another difficulty met'with inthe .operation of mercury boilersis due to the fact that mercury ordinarily does not wet ferrous metal. Ihave.

foundthat wetting of the ferrous metal boiler. walls by mercury liquid maybe accomplished by the adding of certain agents suchas sodium or potassium. An arrangementrand a method of operating mercury .boilers of this kind is covered by my Patent 1,964,592, illed'August 17, 1931,

and assigned to the same assignee as the present application.

Certain inhibitors may form a thick coatingV Von the ferrous metal surfaces in contact with the mercury. Such heavy coatings are undesirable, particularly when formed in verynarrow channels through which the mercury flows because the thick coating may lead to plugging of suchl channels. A further difficulty experienced in the operation of mercury boilers is the formationof v heavy lumps caused by 'the 'oxidationof certain f ingredients such as sodium when added to the mercury. Such lumps may endangerthe operation of a mercury boiler by plugging fluid passages.v There always will be oxidation of agents but the oxides thus formed which constitute waste should not be inthe form of lumpsbut rather in a powdery formiwhich 'does vnot interfere with the ow of mercury through the heating ele-A ments.

One object of the `present invention is to provide anv improved arrangement and method of operating a mercury boiler ofthe type specified above, whereby the'dissolving of ferrous metal" rby the mercury at high temperaturesisfpref. Y,

vented, and satisfactory wetting of the boiler. walls by the mercuryliquid is attained.

Another object of' my invention is to provideV an improved method of and Varrangement for adding inhibitors and wetting agents or substances to theV mercury, whereby the lprotective and wettingv effect of such agents is initiated within a short periodici time. f Other objects Yof my invention areY Athe provision of inhibitors and agents for mercury boil-,- ers which do not cause pluggingv ofy passages by f the formation of oxides. y k ,Y Fora consideration of further objects and features of my invention, yattention is directed to the following Vdescription and the ,claims rappended theretoA in' connection with the accompanying drawing. Y Y In'the drawing, Fig. 1 vis a somewhat diagrammatic view of a mercury boiler embodyingmy invention, and Fig. 21SV a detailfofFig. 1. l In 'the'course of extensive tests and research work konmercury boilers, I havediscovered certain substances which, when added vtof they, mervcury insufficient amounts, prevent substantially completely the dissolving of ferrous metal bythe mercury at the operating temperatureof vthe boiler,lwhich ,at the ,present time is ofthe order of 1000? A Two ofA these substances which have lgivenV very Vsatisfactory results are zirconiumfand 5 titanium. These substancesact primarily as in" hibitors, reducing Vthe dissolving of ferrous metal by the mercury, but they'also actas wetting agentswhen added to thel mercury insufficient amounts. The use of these substances has distinct advantages. They form, when added to the mercury, extremely thinlayers or coatings on or with the ferrous metal walls oftheboiler. These layers or coatings adhere to Y'theboiler surface. They mayalso partly penetrate into the surface Vand form alloys with ferrous metal of the boiler walls. The thickness of these coatings is not increased substantially by the addition kof excessive amounts of these substances. This is important*V in mercury boiler arrangements including a nums ber of heating elements forming narrow passages because layers of "considerable thickness formed in these passagesv by excessive amounts of such substances "would considerably reduce the ow of fluid therethrough, and incertain cases might cause clogging thereof. Thus, the-use of rthese substances-not only inhibits the 'dissolving of ferrous metal, but also assures the' formation of a reasonably uniform layer of extreme thinness of good heat conductivity, and consequently a uniform now of fluid through the various elements of the boiler. Another distinct advantage of zirconium and titanium is that they do not form bulky or voluminous oxides or ferrites which reduce the danger of clogging of the narrow and small diameter passages by the inhibitors themselves. .The oxidation products of zirconium and titanium in mercury boilers formpowdery, dry substances which may be readily removed from the boiler by means of sumps, traps, or the like. One of the most outstanding characteristics of zirconium and titanium, when used as inhibitors, is their effectiveness in very small amounts.

Titanium and zirconium are only slightly soluble in mercury at boiler temperatures. By way of comparison, it has been found that roughly from 10,000 to 100,000 times more aluminum can be held in solution at temperatures from 1000 to 1200 F. than zirconium or titaium. This fact is important in that it prevents extreme concentration at any pointin the boiler; orvirom another viewpoint, it assures more uniform distribu# tion of the inhibitors throughout the different elements of the boiler. Due to thelow solubility of zirconiumY and titanium in mercury, coatings formed on the mercury boiler walls resist redissolution more than. other known inhibitors and the presence of this coating together with the metal in the mercury results in the complete protectiveraction.

VZirconium and titanium' addedto mercury.

f boilers as Vpure metals are present during any or all of the: following states: (a)'In solution in the hot mercury in small amounts; (b)` Deposited as an extremely thin and uniform coating von or alloyed with them'ercu'ry-wetted boiler surfaces and (c) In the form of well wetted, nely divided particles. When theboiler is cooled down then, due to the fact that these metals are so slightly soluble inthe mercury at low temperatures, most of the dissolved metal crystallizes out of the mer-V Y.

cury in theform of very ne particles andrthese particles'are well wetted. 'I'his isV of 'decidedfadvantage because such'wetted crystallized particles u are not as susceptible to attack by oxygen which may leak into the boiler during shut down periods (as single molecules in a dissolved state). In contrast hereto, other inhibitors, suchv asaluminum;` which are'more soluble in mercury, combine with oxygen much more readily than either titanium or zirconium because such` other inhibitors are in molecular state rather than in the form of wetted particles protected by a coating of mercury. Mercury containing zirconium and titanium in amounts sumcient to completely protect a boiler from the dissolving action of the mercury has been kept for days Vin bottleswith air over the mercury without causing serious oxidation of these inhibitors. economy of a mercury boiler are considerably improved by the adding of one of these inhibitors to the mercury. ,Y l

As stated above, either of the elements of the group zirconium and titanium in addition to their effect as inhibitors act as cle-oxidizing agents in` a mercury boiler. I have found that the de-oxidizing action of` these substances, however, may reduce to some extent their inhibiting. effect, par- Y ticularly when used in systems in which considerable amount of oxygen is present.l Also the coating Von the boilerwalls formed by zirconium The reliability and the because thelatter does not properly wet the oxidized coating. I have found that these difllculties are overcome by adding to the mercury togetherwith an inhibitor a de-oxidizing agent which has an affinity to oxygen stronger than that of the inhibitor. If zirconium or titanium are used as inhibitors, I have found that aluminum, magnesium and calcium when added to such inhibitor act as strong de-oxidizing agents.

vOrdinarily these substances, aluminum, magnesium and calcium, act as inhibitors when used alone, that is, prevent the mercury from dissolving ferrous metal walls at highv temperatures.

' The use of magnesium or calcium as de-oxidizing agent is preferable because neither forms a coating on the boiler walls when used together with zirconium or titanium.

The use of strong de-oxidizing agents, such as magnesium and calcium, in mercury boilers increases the -economy of the process. These agents reduce oxides in the system, in particular oxides formed by zirconium and titanium. Hence, the entire amount of zirconium or titanium added to the mercury is maintained in an effectivestate in which such substances form coatings and thereby inhibit the dissolving action of mercury at high temperatures. on ferrous metal. The oxides of zirconium and titanium being ineffectiveV as inhibitors, it is desirable to vmaintain such in- Ihibiting substances in a metallic state. Thus,

with the addition of strongde-oxidizing agents, the waste of inhibitors due lto oxidation is avoided. Practically complete Vstoppage of dissolving of ferrous metal by mercury has been accomplished'with an amount of inhibitor equal tto one part by weight in 100,000 parts of mercury. In cases in which the oxidizing agents, such as sodium, are used to effect wetting of the boiler sursubstances reduces oxides formed by sodium or the like and thereby breaks up large lumps of sodium oxides to form a powder,Y thus preventing ,the plugging of iluid passages.

, Only comparatively small amounts of zirconium or titanium are needed for, complete boiler 'protection. For instance, in a large lcommercial` during operation.

summarizing, complete protection of a mercury boiler may be obtainedby adding to the mercury one of the elements of the group zirconium and titanium and one/of the elements of the group magnesium and calcium. The addition Vof these substances inhibits the dissolving of ferrous metal, causes wetting of the boiler sur- .faces by the` mercury and reduces oxides in the boiler into harmless and readilyremovable dry f faces by the mercury, the addition of magnesiumV or calcium has the advantagethat either of theseA powders. 'u Such complete protection over a, long period ofv time may be attained by periodic tests .mercury Such analysis may be made daily, de-

pending upon the conditions of the boiler. Satisfactory results have been obtained, by maintaining concentration of zirconium metal in the mercury above .0002% by weight and of magnesium above .001% by Weight. It is preferable to mainmittently operated and which are'subject to air infiltration. Whenever -these analyses show a deficiency of either the inhibiting or reducing substance, the necessary amount of such substances are added to make up the deficiency.

The protective action'or effect of titanium or zirconium is complete as soon as the inhibitor is uniformly distributed throughout the boiler system and has formed a coating on or with the ferrous metal walls. The time lag between .the adding of these substances or inhibitorsand their complete effectiveness o'r protective actions, that is, the formation of a coating on or with the boiler walls, is reduced in accordancewith an improved method of adding 'these substances. Before describing the method itself, attention is directed to the fact that zirconium and titanium in their commercial form are not chemically pure, but include certain impurities, and what is more important, they are covered with a thin layer of oxide. If added in this form directly to the mercury in a mercury boiler, it obviously takes a certain period of time until the Voxide im. is broken down or removed from the particles and the elements are wetted by the mercury. yI'his undesirable time lag is reduced in accordance with my invention by prewetting the substances to be added to the mercury boiler by means of mercury liquid. It is also known `that nonwetted particlesare carried outqof the lboiler with. the vapor whereas wetted particles are not carried out except in mercury liquid mechanically suspended in the mercury vapor, such suspended liquid 4being negligible in the system and maybe substantially eliminated by the provision of known liquid vapor separating means.Y For the purpose of prewetting, zirconium or titanium Aare put into a hermetically sealed container or bomb together with a certain amount of mercuryand heated therein in the'absence of air to Lprevent oxidation of the metals. Heating of the mixture is necessary to effect wetting 'ofthe substances.

by the mercury. This prewetting may be accelerated if the substance suchi as zirconium or titanium is added to the mercury as powder. As

stated before, titanium and zirconium have a low solubility in mercury. By adding these elements in the form of powder to mercury liquid large surfaces, as compared to the weight or volume of these elements, are contacted by the mercury. This is important also when titanium and zirconium are added in nonwetted form directly to the mercuryboiler because it limits theV temperature of the order of about `1000""F.4 `To Y exclude air or oxygen during the prewetting, the

mixture is preferably placed in' a hermetically sealed bomband to accelerate theV wetting process, the bomb is preferably moved,"ti1ted, or yoscillated, in a rocking furnace for a period vof 50 `to 100 Yhours to'make sure that the vparticles are well wetted.

p vA further important feature Yof my invention` is the provision of means forand a method of protecting a mixture of mercury and wetted zirconiumY or like substance against oxidation and.

the consequent de-wetting of the substance, espe-Y cially whenv these are highly concentrated.. I

have found that this may be accomplished by adding to the mixture of mercuryand titanium or like -substance asmallamount of zinc, copper,

or like -lm stabilizing agent. A piece or particle of zirconium or titanium .is prewetted, when its surface has beenbroughtinto intimate contact with the mercury. The mercury-'then has a strong tendency to adhere to such surface. A prewetted surface is ordinarily rapidly de-wetted when such particle is. exposed to oxygen or air.

The de-Wetting of la wetted particle is considerably reduced by the provision of a film stabilizing substance in the mercury. As said before, a particle is wetted when a film of mercury adheres strongly to the surface of the particle. Such film of mercury may be stabilized by a small amount of zinc or copper sothat a wetted vparticle may be exposed to air for a considerable period of time. The surface film Atoughening substance may be added to the mercury during the prewetting process. Satisfactory results have been obtained with mixtures comprising about 18 parts by weight of. mercury, 1 Vpart of titanium and 1/6 part of zinc. Such mixture is preferably sealed in-a low carbon 4steel tube orrbormb and heated at 1000" F. for aboutV 50 to 100 hours in a` rocking In arrangements in `which a strong de-,oxidizf l Y ing agent, such as magnesium-.or ycralcium,`is .to

'74o'. furnace. The tubes varekept sealed `until themixbe used in the boileratogether with `zirconium Vor titanium, the mixture of .mercury and wetted zirconium may be protectedagainst oxidation byV adding to it .either magnesium or calcium. In this case I have obtained good results by loading a bombwith 18 to 54Y parts bykweight of mercury to one part of titanium or zirconium with a small amount of magnesium or calcium. Insuch case a stabilizing substance, such as zinc or copper, may be dispensed with, provided great care is taken in supplying the mixture contained in the bomb to the boiler. The great afiinity ofmagnesium or calcium for oxygen allows this process to be carried out in ordinary low carbon steel bombs at a temperature of the order of 900 F.

The arrangement illustrated in the drawing comprises a drum I0 offerrous metal covered by lagging or like heat insulating material Il held in place by a cover i2. The drum is partly nlled with mercury liquid I3 to which has been added an inhibitor or` substance as hereinbefore de-l scribed. A vfiller block i4 is provided in the liquid space of the drum for displacing Va. portion ofthe liquid to minimize the amount of liquid necessaryfor operating the boiler." Fastened to the lower portion of the drum I0 are a plurality of heating tubes i5 made from ferrous metal. Each 22 is fastened at its upper end to a baille plate 23,

disposed within the drum I and with its lower end extends into the passage 20 defined by the inner wall of the core. During operation, mercury liquid is conducted from'the space above a bafiie plate 23 in the drum III through the sleeve 22 into the passage 20, whence it iiows into the passage 2| defined between the outer tube I6 and the outer wall I9. Heat is conducted to the tubes and the drums by `radiation and conduction. The liquid contained in the outer passage 2| is partly evaporated and conducted to the drum. 'Ihe provision of a double-walledcore in the tube minimizes the direct heat transfer from the outer passage 2 I, which may be termed thevapor passage,

into the inner passage 20 which may be termed the liquid passage. This results in a differential pressure between the fluids conducted through the two passages, to the effect that a steady flow or circulation of fluid through said passages takes place. The vapor produced in the boiler is conducted through a conduit 24 to a turbine 25whence the exhaust is received by a condenser 26 having cooling means 28. Y The condensate is returned to the drum by means of a conduit 23 connected to the condenser 26 and a pipe 30 between the conduit 29 and the drum I0. l

Besides .the drums VII) and the heating tubes connected thereto, other heating units or elements may beprovided. In the present instance I have shown'a heating unit 3I having a header 32 communicating with the vrliquid in the'drum through a conduit 33. 'Ihe heating unit `3I comprises a down-tube 34 connecting the header 32 to a lower header 35, located external a wall 36 of the furnace." The lower header 35 is connected to the lower ends of up-tubes 31 locatedinside the wall 36 of the furnace and having their upper ends projecting through the furnace wall and connected to the upper header 32. The tubes 31 form a wall screen for thefurnace wall 36;

During operation, mercury liquid contained in the tubes 31 is heatedto form vapor. in these tubes rises and flows into the upper header 32. The vapor thus formed is conducted through the conduit 33 to the drurn and the liquid is recirculatedthrough the down-tubes 34 and the up-tubes 31. To prevent the up-stream from the tubes 31 from interfering with the liquid flowing into tubes 34, a bafiie plate 38 is providedin the upper header 32. Y l.

The arrangement for adding inhibiting and wetting substances in accordance with my invention comprises a standpipe 40 connected at the lower end to an intermediate point of thedowntube 34. 'I'he standpipe includes a lower valve 4I and an upper valve 42 and has an upper portion formed to define a funnel 43.V A substance may be added to the boiler during operation by first opening the valve 42, then pouring the substance into the pipe 40, thereafter Vclosing the valve 42, and finally opening the valve 4I to permit the substance to flow into the down-tube 34 to be carried into the boiler system. To prevent large pieces from being supplied Qinto the boiler, a strainer 44 is provided at the lower end of the funnel 43.

`system due to their light weight.

The fluid Zirconium and titanium, when added in the form of powder, have a tendency to float on the surface of the mercury, and difficulties have been experienced in forcing these substances into the` These difiiculties are overcome by the provision of a tank 45 for containing mercury liquid 46 connected to the funnel 43by a conduit 41 including a valve 48. During the adding of powdered titanium, zirconium or like substance, the valve 48 is opened together Vwith the valve 42, so that the substance is flushed into the tube 40 by a stream of mercury liquid discharged from the tank 46. The mercury is preferably supplied from thetank 46 in dry form. Water is separated from the mercury by the provision of heating means, in the present instance a steam coil 49 disposed within the tank 46.

The system also includes means permitting the removal of boiler fluid for analysis to assure the presence of an eflicientv amount of inhibiting and oxygen-reducing substances in the active state. This means has been shown in the drawing as comprising a pipe 50 connected to down-tube 34 and including two valves I and 52 arranged in series. With this arrangement, boiler fluid may be removed during operation by opening the valve 5I to permit boiler uid to fiow into the portion Vof the pipe 50 betweenthe valves 5I and 52.

Thereafter the valve 5I is closed and the valve 52 opened.

Everyv possible precaution should be taken to eliminate, conditions allowing lcontact between the inhibitors and oxygen r oxides in order to have at all times in the mercury these inhibitors in metallic state in the boiler. VAll parts of the system must be carefully sealed. Preferably nitrogen or other inert gas is leaked into the system during shut-down periods.

While I have described my invention particularlyin connection withV mercury boilers, it is not limited thereto necessarily but maybe utilized Awherever rconditions are met with which make it desirable to overcome the tendency for mercury to dissolve ferrous metal at high temperatures.

In accordance with the provisions of the patent statutes, I have described the principleV of operation of my invention, together with a particular method and apparatus which I now'consider to represent the best embodiment thereof, but I de-Y lower temperature, said boiler beingcharged withl mercury to which has been added an inhibitor a metal which has very low Vsolubility in mercury and at the operating temperature of the boiler forms an extremely thin uniform coating on the boiler surfaces contacting the mercury, and the de-oxidizing agent having an ainity to oxygen stronger than that of the inhibitor.

3. A mercury boiler having ferrousmetal tubes through which mercury circulates between a. region of higher temperature and a region of lower temperature, said boiler being charged with mercury to which has been added an element of the group titanium and zirconium.v

4. A mercury boiler having ferrous metal tubes through which mercury circulates between a region of higher temperature and a region of lower temperature, said boiler being charged with mercury to which has been added an element of the group titanium and zirconium together with a de-oxidizing agent with greater ainity to oxygen than either element of saidA group.

5. A mercury boiler having ferrous metal tubes through which mercury circulates between a region lof higher temperature and a region of lower temperature, said boiler being charged with mercury to which has been added an element of the group titanium and zirconium together with at least one element of the group magnesium and calcium. f

6. A mercury boiler having ferrous metal tubes through which mercury circulates at high temperature, said boiler being charged with mercury to which has been added an element of the group titanium and zirconium of an amount of more than .0001% by weight of mercury.

7. A mercury boiler having ferrous metal tubes through which mercury circulates at high` temperature, said boiler being charged with mercury to which has been added an element of the group titanium and zirconium in an amount of the order of .0002% by weight of the mercurytogether with an'amount of an element of the group magnesium and calcium of the order of more than .O01 by weight of mercury.

8. An operating uid for containers having ferrous metal walls subject to high temperatures during operation comprising mercury and a small amount of a substance associated with the mercury which substance forms an extremely thin coating on ferrous metal when contacted by the uid at high temperature, and a small amount of a reducing agent to prevent oxidation of said substance and to reduce oxides when added to the container.

9. A composition for operating boilers havingt ferrous metal walls comprising substantially en` tirely mercury and a small amount of a substance forming a thin dissolution resistant layer on ferrous metal at high temperature and a small amount of one of the elements of the group magnesium and calcium.

10. A mercury boiler including the combination of a container made from ferrous metal, mercury liquid contained in the container, and means to prevent dissolving of ferrous metal by the merl cury at the operating temperature of the boiler and to effect wetting of the boiler surfaces by the mercury liquid, said means comprising one of the elements of the group zirconium and titanium in the mercury liquid of an amount of about .04% by weight of the mercury.

l1. A mercuryboiler includingy the combination of a container made from ferrous metal, mercury liquid contained in the container, means to prevent dissolving of ferrous metal by the mercury at the operating temperature of the boiler and to effect wetting of the boiler surfaces by the mercury liquid, said means comprising one of the eleweight of the mercury.

ments of the group zirconium and titaniumin the mercury liquid, and means to maintain the concentration of such element above .0001% by 12. A mercury boiler including the combination of a container made from ferrous metal, mercury liquid contained in the container, means toipre-v vent dissolving of ferrous metal by the mercury at the operating temperature of the boiler and to effect wetting of the boiler surfaces by the mercury liquid, said means comprising one of the elements of the .group zirconium and titanium in the mercury liquid, and means including a valved conduit connected `to the boiler for supplying one l of said elements to the boiler during operation thereof to maintain the concentration of such element above .0001'% by weight of the mercury and one of the elements of the group magnesium and calcium lin the mercury liquid.

13. In Atheoperation of a mercury boiler having ferrous metal walls, the method of adding to the mercury an inhibitor in powderedform and i the adding of one of the elements of the group i magnesium and calcium to prevent oxidation of the inhibitor.

14. In the operation of va mercury boiler having ferrous metal tubes through which mercury liquid is circulated during operation, the method of adding to the mercury a mixture in powdered form,which mixture includes an element of` the group titanium and zirconium and an element of the group calcium and magnesium.

15. AV substance for protecting mercury containers made Vfrom ferrous metal against dissolving of the ferrous metal by the mercury at high temperature, such substance including a pretreated mixture of'avl smallI amountof an in -v .@hibitor anda comparatively large amount of mercury together withA a reducing agent to prevent oxidation Aof the inhibitor.

16.V The method of preparing a workinguid for a mercury boiler -having ferrous metal tubes v with surfaces contactedby 'heated mercury during operation-which method comprises mixing a small amount of an inhibitor whichJis wetted by mercury when heated with a comparatively large amount of mercury liquid, heating the mixture in the absence of oxygen to cause the mercury to wet the inhibitor and thereafter adding the mixture to the mercury in the boiler.

17. 'I'he method of preparing a working fluid for a mercury boiler having ferrous metal tubes with surfaces contacted by heated mercury during operation, which method comprises mixing a small amount of one of the elements of the group zirconium and titanium with a large amount of mercury, and heating the mixture in a hermetically sealed vessel lto effect wetting of the element by the mercury. l

18. The method of preparing a working fluid for a mercury boiler having ferrous metal tubes with surfaces contacted by heated mercury during operation, which method comprises mixing powder of one of the elements of the group titaniumY and zirconium with mercury liquid, agitating the mixture, heating the mixture during agitation in the absence of oxygen, and supplying the mixture to the liquid in the boiler'.v

19. The method of preparing a working fluid heating the mixture and supplying it to the mercury in the boiler.

20. The method of preparing a working fluid for a mercury boiler having ferrous metal tubes with surfaces contacted by heated mercury during operation, which method comprises mixing an inhibitor with a reducing agent of greater afhnity to oxygen than the inhibitor, heating the `mixture and supplying it to the mercury liquid in the boiler.

21. The method of preparing a working fluid for a mercury boiler having ferrous metal tubes with surfaces contacted by heated mercury during operation, which method comprises mixingY an element of the group zirconium and titanium with at least one element of the group zinc, copper, magnesium and calcium and a comparatively large amount of mercury liquid, and supplying the mixture to the liquid in the boiler.

22. The method of preparing a working uid for a mercury boiler having ferrous metal tubes with surfaces contacted by heated mercury during operation, which method comprises mixing an element of the group zirconium and titanium and an element of the group magnesium and calcium with a large amount of mercury liquid, heating the mixture at a temperature of the order of 900 F. and supplying the lmixture to the mercury liquid in the boiler.

,if 23. A fen-ous metal container through which ,gimercury liquid is circulated at high temperature.'

said container being charged with mercury, an element of the group zirconium and titanium and a strong oxygen-reducing agent.

V'24. A mercury boiler having tubes madev from ferrous metal through which mercury liquid is circulated at high temperature, said boilerl being charged with an inhibitor which is wetted by mercury when heatedrto form a thin coating on the boiler walls to prevent dissolving'thereof-by l the action of mercury at high temperature and an excess of inhibitor to maintain the coatingl and a. small amount of one of. the elements ofV the group zinc and copper to stabilize the protective layer formed on the ferrous metal and .circulated during operation, and means for conducting inhibiting and oxygen reducing substances into the tubes during operation of the boiler, said means including a standpipe connected to one of the tubes and including lower and upper valve means.

27. A mercury boiler comprising tubes made from ferrous metal through which mercury is circulated during operation, means Afor conducting a substance into the tubes during operation of the boiler, said means including a standpipe connected at its lower end to one of the tubes, a lower and upper valve in the standpipe, a funnel secured to the upper end of the standpipe, and a sieve intermediate the funnel and the upper valve to prevent large solid pieces from being conducted into the standpipe.

28. A mercury b'oiler having heating units made from ferrous metal for heating and operating mercury liquid, said units including down tubes disposed outside the boiler, and means for conducting an inhibitor into the heating `units during operation, said means including a standpipe having a lowerV end connected to an intermediate portion of the down tube, a lower and uppervvalve in the standpipe, a funnel secured to theupper end of the standpipe, and means for flushing solid inhibitors from the funnel into the standpipe, said last-named means comprising a container for liquid mercury connected to the upper end of the standpipe, and means for drying mercury liquid in the container.

ANTHONY J. NERAD. 

